1. Field of the Invention
The invention concerns an automatic boresighting device for an optronic system comprising a laser and two image sensors working respectively in two different ranges of spectral sensitivity. For example, the system includes: a laser telemeter, a distance measuring device, and a tracking and identification device. These devices include a common optical channel constituted notably by means for directing a common line of sight. The boresighting consists in superimposing the optical axes of these three devices so that they have a common line of sight. In general, a boresighting performed on a test stand, in the factory, is not preserved after a certain amount of time of operational use of the system. It should be possible to redo the boresighting during operational use, as a particular stage of operation, and the boresighting should be automatic. Moreover, it is desirable to be able to change a sub-assembly of the system, notably the laser telemeter, without having to redo the manual adjustments.
The invention more particularly concerns the optronic systems in which the distance measuring device and the tracking and identification device respectively include two image sensors, working respectively in two different ranges of spectral sensitivity, having no common wavelength. For example, the distance measuring device has an image sensor working in the 3-5 micrometer band or in the 8-12 micrometer band to localize a target in elevation and in bearing, while the identification and tracking device has an image sensor working in the 0.7 to 0.9 micrometer band, that is, in the visible and near infra-red radiation band. In certain applications, the laser telemeter emits a wavelength that belongs to none of these ranges of spectral sensitivity, for example a wavelength of 1.54 micrometers.
2. Description of the Prior Art
The U.S. Pat. No. 4,155,096 describes an automatic boresighting device for an optronic target designator system, comprising an image sensor and a laser. The laser has a 1.06 micrometer wavelength, which belongs to the range of spectral sensitivity of the image sensor extending from 0.4 to 1.1 micrometers. This boresighting device includes a cube corner, towards which the line of sight is directed, during the boresighting. The boresighting further consists in turning on the laser. The cube corner reflects a fraction of the laser beam towards the image sensor. The laser beam therefore forms a light spot on the image sensor. An image processing operation makes it possible to determine the distance between this spot and the centre of the image sensor and to deduce a boresighting correction therefrom. This known device cannot be used when the laser does not have a wavelength within the range of spectral sensitivity of the image sensor.
The U.S. Pat. No. 4,422,758 describes a boresighting device for an optronic target-designation system. This system comprises: a laser working at 1.06 micrometers, an image sensor in the visible radiation range and an image sensor in the infrared radiation range. The boresighting device includes a collimator towards which the line of sight is pointed during boresighting. A refractory target is placed in the focal plane of the collimator. The laser is turned on and its radiation is focused on to the target to create a hot spot emitting visible rays and infra-red rays. The image of this hot spot is detected simultaneously by the two image sensors and enables the measurement of the errors of boresighting of the axis of the laser with respect to the axes of the two image sensors. This device has the drawback of making it necessary to focus a substantial amount of energy on the refractory target. It is not easy to obtain a very hot target when the laser has only medium power or low lower. Moreover, the use of the laser leads to a certain degree of energy consumption and to a certain reduction in the lifetime of the laser.